U.S. patent application number 14/579802 was filed with the patent office on 2015-07-02 for illumination device and image reading device.
The applicant listed for this patent is KYOCERA Document Solutions Inc.. Invention is credited to Katsuhiko Okamoto.
Application Number | 20150189117 14/579802 |
Document ID | / |
Family ID | 53483335 |
Filed Date | 2015-07-02 |
United States Patent
Application |
20150189117 |
Kind Code |
A1 |
Okamoto; Katsuhiko |
July 2, 2015 |
ILLUMINATION DEVICE AND IMAGE READING DEVICE
Abstract
An illumination device includes a light source and a columnar
light guide including: an incident surface provided at least one
longitudinal end of the light guide and allowing light emitted from
the light source to enter the light guide therethrough; a diffusing
surface which forms one side surface of the light guide extending
along an optical axis of the incident light entering the light
guide through the incident surface and has a row of light diffusion
patterns provided to diffuse the incident light; and an exit
surface located opposite to the diffusing surface, extending along
the optical axis, and allowing light diffused by the diffusing
surface to exit the light guide therethrough. The light diffusion
patterns have a prismatic shape rising toward the exit surface and
are provided on the diffusing surface from D.sup.1/2.times.8 or
greater distance from the incident surface where D represents the
diameter of the light guide.
Inventors: |
Okamoto; Katsuhiko; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA Document Solutions Inc. |
Osaka |
|
JP |
|
|
Family ID: |
53483335 |
Appl. No.: |
14/579802 |
Filed: |
December 22, 2014 |
Current U.S.
Class: |
358/475 ;
362/608 |
Current CPC
Class: |
G02B 6/0018 20130101;
G02B 6/0025 20130101; H04N 1/02815 20130101; G02B 6/001 20130101;
G02B 6/0038 20130101 |
International
Class: |
H04N 1/028 20060101
H04N001/028; F21V 8/00 20060101 F21V008/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2013 |
JP |
2013-270009 |
Claims
1. An illumination device comprising: a light source; and a
columnar light guide including an incident surface provided at
least one of both longitudinal ends of the light guide and allowing
light emitted from the light source to enter the light guide
therethrough, a diffusing surface forming one side surface of the
light guide extending in a direction of an optical axis of the
light entering the light guide through the incident surface, the
diffusing surface having a plurality of light diffusion patterns
provided in a row to diffuse the light having entered the light
guide through the incident surface, and an exit surface located
opposite to the diffusing surface to extend in the direction of the
optical axis and allowing the light diffused by the diffusing
surface to exit the light guide therethrough, wherein the light
diffusion patterns have a prismatic shape rising toward the exit
surface and are provided in a row on the diffusing surface from
D.sup.1/2.times.8 or greater distance from the incident surface
where D represents the diameter of the light guide.
2. The illumination device according to claim 1, wherein the
longitudinal end of the light guide at which the incident surface
is provided is curved in a direction away from the exit surface, a
curved reflective surface is provided between the incident surface
and the exit surface, and the light guide is configured so that
light incident on the incident surface is totally reflected at the
reflective surface to progress toward a middle region of the light
guide.
3. The illumination device according to claim 1, wherein each of
both end surfaces of the light guide located at both the
longitudinal ends thereof is the incident surface.
4. An image reading device comprising an illumination device, an
original glass plate, and a light-receiving element, wherein the
illumination device comprises: a light source; and a columnar light
guide including an incident surface provided at least one of both
longitudinal ends of the light guide and allowing light emitted
from the light source to enter the light guide therethrough, a
diffusing surface forming one side surface of the light guide
extending in a direction of an optical axis of the light entering
the light guide through the incident surface, the diffusing surface
having a plurality of light diffusion patterns provided in a row to
diffuse the light having entered the light guide through the
incident surface, and an exit surface located opposite to the
diffusing surface to extend in the direction of the optical axis
and allowing the light diffused by the diffusing surface to exit
the light guide therethrough, the light diffusion patterns have a
prismatic shape rising toward the exit surface and are provided in
a row on the diffusing surface from D.sup.1/2.times.8 or greater
distance from the incident surface where D represents the diameter
of the light guide, and the light-receiving element is configured
to receive light reflected on an original document placed on the
original glass plate by irradiating the original document with
light having exited the light guide through the exit surface.
5. The image reading device according to claim 4, wherein an image
reading range in a main scanning direction on the original glass
plate is set between two positions a predetermined distance
inwardly from both ends of the row of the light diffusion patterns.
Description
INCORPORATION BY REFERENCE
[0001] This application claims priority to Japanese Patent
Application No. 2013-270009 filed on Dec. 26, 2013, the entire
contents of which are incorporated by reference herein.
BACKGROUND
[0002] The present disclosure relates to illumination devices with
a light guide and image reading devices with a light guide and
particularly relates to a technique in which light having entered
the light guide through the incident surface thereof is diffused
toward the exit surface of the light guide.
[0003] In image reading devices, such as a scanner, image reading
is performed by applying light to an original document from which
an image is to be read and receiving, at a light-receiving element,
reflected light from the original document. In recent years, from
the viewpoint of energy saving, downsizing, and so on, there
emerge, as illumination devices for applying light to an original
document from which an image is to be read, those employing a line
light source in which a light source formed of a light-emitting
element, such as an LED (light emitting diode), is combined with a
light guide configured to guide light emitted from the light
source. A plurality of light diffusion patterns are provided in a
row on a surface (diffusing surface) of the light guide opposite to
an exit surface thereof through which light exits the light guide.
The light diffusion patterns are configured to diffuse light having
entered the interior of the light guide to allow linear
illumination light to exit the light guide toward the original
document from which an image is to be read.
SUMMARY
[0004] A technique further modified from the above known technique
is proposed as an aspect of the present disclosure.
[0005] An illumination device according to one aspect of the
present disclosure includes a light source and a light guide.
[0006] The light guide is a columnar light guide including: an
incident surface provided at least one of both longitudinal ends of
the light guide and allowing light emitted from the light source to
enter the light guide therethrough; a diffusing surface forming one
side surface of the light guide extending in a direction of an
optical axis of the light entering the light guide through the
incident surface, the diffusing surface having a plurality of light
diffusion patterns provided in a row to diffuse the light having
entered the light guide through the incident surface; and an exit
surface located opposite to the diffusing surface to extend in the
direction of the optical axis and allowing the light diffused by
the diffusing surface to exit the light guide therethrough.
[0007] The light diffusion patterns have a prismatic shape rising
toward the exit surface and are provided in a row on the diffusing
surface from D.sup.1/2.times.8 or greater distance from the
incident surface where D represents the diameter of the light
guide.
[0008] An image reading device according to another aspect of the
present disclosure includes the aforementioned illumination device
and a light-receiving element.
[0009] The light-receiving element is configured to receive light
reflected from an original document irradiated with light having
exited the light guide through the exit surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a front cross-sectional view showing the structure
of an image forming apparatus equipped with an image reading device
according to one embodiment of the present disclosure.
[0011] FIG. 2 is an internal side view showing a schematic
structure of the image reading device according to the one
embodiment of the present disclosure.
[0012] FIG. 3 is a perspective view showing an illumination device
according to the one embodiment of the present disclosure.
[0013] FIG. 4 is a perspective view showing light diffusion
patterns provided in a row on a diffusing surface located inside of
a light guide in the one embodiment of the present disclosure.
[0014] FIG. 5 is a perspective view showing in enlarged scale the
light diffusion patterns provided in a row on the diffusing surface
in the one embodiment of the present disclosure.
[0015] FIG. 6 is a view showing optical paths of light diffused by
the light diffusion patterns provided in a row on the diffusing
surface in the one embodiment of the present disclosure.
[0016] FIG. 7 is a view showing the relative positions of the light
guide and an original glass plate in the one embodiment of the
present disclosure.
[0017] FIG. 8 is a perspective view showing an illumination device
included in an image reading device of Comparative Example 1.
[0018] FIG. 9 is a graph showing reflected light diffusion
distributions in the sub-scanning direction produced by a light
guide in Comparative Example 1.
[0019] FIG. 10 is a graph showing intensity densities of direct
light and indirect light when the diameter of the light guide in
Comparative Example 1 is 4 mm and 6 mm.
[0020] FIG. 11 is a perspective view showing the shape of light
diffusion patterns provided in a row on a diffusing surface of a
light guide in Comparative Example 2.
[0021] FIG. 12 is a view showing the relative positions of a light
guide and an original glass plate in an image reading device of
Modification 1.
[0022] FIG. 13 is a side view showing a light guide included in an
image reading device of Modification 2.
DETAILED DESCRIPTION
[0023] Hereinafter, a description will be given of an illumination
device according to one embodiment of the present disclosure and an
image reading device with the illumination device with reference to
the drawings. FIG. 1 is a front cross-sectional view showing the
structure of an image forming apparatus equipped with the image
reading device according to the one embodiment of the present
disclosure.
[0024] The image forming apparatus 1 according to the one
embodiment of the present disclosure is a multifunction peripheral
having multiple functions including, for example, a copy function,
a print function, a scan function, and a facsimile function. The
image forming apparatus 1 is made up so that an apparatus body 2
thereof includes an operating section 47, an image forming section
120, a fixing section 13, a paper feed section 14, a document feed
section 6, an image reading device 5, and so on.
[0025] The operating section 47 is configured to receive operator's
commands for various types of operations and processing executable
by the image forming apparatus 1, such as a command to execute an
image forming operation and a command to execute an image reading
operation. The operating section 47 includes a display 473
configured to display operation guidance and so on for the
operator.
[0026] In an image reading operation of the image forming apparatus
1, the image reading device 5 optically reads an image of an
original document being fed from the document feed section 6 or an
image of an original document placed on an original glass plate 161
to generate image data. The image data generated by the image
reading device 5 is stored on an internal HDD, a network-connected
computer or the like.
[0027] In an image forming operation of the image forming apparatus
1, the image forming section 120 forms a toner image on a recording
paper sheet P serving as a recording medium fed from the paper feed
section 14, based on image data generated by the image reading
operation, image data received from a network-connected computer or
a user terminal, such as a smartphone, or image data stored on the
internal HDD. Each of image forming units 12M, 12C, 12Y, and 12Bk
of the image forming section 120 includes a photosensitive drum
122, a developing device (not shown) operable to supply toner to
the photosensitive drum 122, a toner cartridge (not shown) for
holding toner, a charging device (not shown), an exposure device
(not shown), and a primary transfer roller 126.
[0028] In the case of color printing, the image forming unit 12M
for magenta, the image forming unit 12C for cyan, the image forming
unit 12Y for yellow, and the image forming unit 12Bk for black of
the image forming section 120 form respective toner images on their
respective photosensitive drums 122 through charging, exposure, and
developing processes based on respective images of respective
different color components constituting the above image data and
then allow their respective primary transfer rollers 126 to
transfer the toner images to an intermediate transfer belt 125
mounted around a drive roller 125A and a driven roller 125B.
[0029] The outer peripheral surface of the intermediate transfer
belt 125 is set to an image carrying surface to which a toner image
is to be transferred. The intermediate transfer belt 125 is driven
by the drive roller 125A while engaging against the peripheral
surfaces of the photosensitive drums 122. The intermediate transfer
belt 125 endlessly runs between the drive roller 125A and the
driven roller 125B while synchronizing with the rotation of each
photosensitive drum 122.
[0030] The toner images of different colors transferred to the
intermediate transfer belt 125 are superposed each other on the
intermediate transfer belt 125 by controlling their transfer
timings, resulting in a multicolor toner image. A secondary
transfer roller 210 transfers the multicolor toner image formed on
the surface of the intermediate transfer belt 125, at a nip N
between the secondary transfer roller 210 and the drive roller 125A
with the intermediate transfer belt 125 in between, to a recording
paper sheet P conveyed from the paper feed section 14 along a
conveyance path 190. Thereafter, the fixing section 13 fixes the
toner image on the recording paper sheet P by the application of
heat and pressure. The recording paper sheet P on which the
multicolor image has been fixed by the completion of the fixing
treatment is discharged to a paper output tray 151.
[0031] The paper feed section 14 includes a plurality of paper feed
cassettes. A control section (not shown) rotationally drives a
pick-up roller 145 of the paper feed cassette containing recording
paper sheets of the size designated by an operator's command and
thereby allows the pick-up roller 145 to feed a recording paper
sheet P contained in the paper feed cassette toward the nip N.
[0032] Next, a description will be given of the structure of the
image reading device 5. FIG. 2 is an internal side view showing a
schematic structure of the image reading device 5.
[0033] The image reading device 5, as shown in FIG. 2, includes an
optical scanning device 7 and an image pickup unit 8.
[0034] The optical scanning device 7 includes a first optical
system unit 71 and a second optical system unit 72. The first
optical system unit 71 includes an illumination device 10 and a
first mirror 711. The illumination device 10 is disposed facing and
below the original glass plate 161 in order to illuminate a reading
surface of an original document, i.e., illuminate above. The
illumination device 10 includes a columnar light guide and a light
source disposed at a longitudinal end of the light guide, as will
hereinafter be described in detail. The illumination device 10
extends in a depth direction of FIG. 2. The direction of extension
of the illumination device 10 is a main scanning direction during
image reading.
[0035] The first mirror 711 is configured to receive light
reflected on the image reading surface of the original document
placed on the original glass plate 161 by the application of light
of the illumination device 10 to the original document and
horizontally redirect the reflected light. The first mirror 711 is
disposed below the original glass plate 161. The illumination
device 10 and the first mirror 711 are mounted to an unshown
support member.
[0036] The second optical system unit 72 includes a second mirror
721 and a third mirror 722. The second mirror 721 is configured to
receive light reflected by the first mirror 711 of the first
optical system unit 71 and redirect the reflected light
substantially vertically downward. The third mirror 722 is
configured to substantially horizontally redirect the reflected
light from the second mirror 721 to guide it toward the image
pickup unit 8. The second mirror 721 and the third mirror 722 are
mounted to an unshown support member.
[0037] The illumination device 10 and the mirrors provided in the
first and second optical system units 71, 72 have an elongated
shape extending in the main scanning direction and having a length
substantially equal to the length of the original glass plate
161.
[0038] The image reading device 5 is internally provided with an
unshown traveling rail for use to guide the movement of the optical
scanning device 7 in the direction of the arrows in FIG. 2. Thus,
the optical scanning device 7 equipped with the first and second
optical system units 71, 72 can reciprocate in a sub-scanning
direction (a direction perpendicular to the main scanning
direction), i.e., in the direction of the arrows in FIG. 2, and in
parallel with the surface of the original glass plate 161 to enable
reading of image information of the entire reading surface of the
original document placed on the original glass plate 161.
[0039] The image pickup unit 8 is fixed to a lower portion of the
interior of the image reading device 5. The image pickup unit 8
includes an imaging lens 81 as an optical element and an image
sensor 82 including a light-receiving element. The light reflected
on the reading surface of the original document and then reflected
by the third mirror 722 of the second optical system unit 72 enters
the imaging lens 81. The imaging lens 81 forms an image of the
reflected light on a surface of the image sensor 82 provided
downstream in the optical path. The image sensor 82 is configured
to generate a voltage indicating and according to the intensity of
light received at the light-receiving element and output the
voltage to the unshown control section. In this manner, using the
image sensor 82, the image of the original document to be read can
be read by the image reading device 5.
[0040] Next, a description will be given of the illumination device
10 included in the image reading device 5. FIG. 3 is a perspective
view showing the internal structure of the illumination device
10.
[0041] The illumination device 10 includes a light guide 11 and a
light source 12.
[0042] The light guide 11 extends in a direction of the optical
axis of light entering the interior of the light guide 11 from the
light source 12. Since the light guide 11 extends in the main
scanning direction as described previously, the direction of the
optical axis coincides with the main scanning direction. The light
guide 11 is formed of, for example, a resin-made light transmissive
member and defined by an incident surface 18, an exit surface 17,
and a diffusing surface 15. The light guide 11 is made by, for
example, injection molding in which molten resin is injected into a
mold.
[0043] The incident surface 18 is a surface of the light guide 11
allowing light emitted from the light source 12 to enter the light
guide 11 therethrough and at least one of both the longitudinal end
surfaces of the light guide 11 provides the incident surface 18. A
description in this embodiment will be given of the case where only
one of the longitudinal end surfaces is the incident surface 18.
The light source 12 is mounted on the incident surface 18. Light
emitted from the light source 12 enters the interior of the light
guide 11 through the incident surface 18.
[0044] The exit surface 17 extends in the main scanning direction
and forms one side surface of the light guide 11. In this
embodiment, the exit surface 17 forms a top surface of the light
guide 11. The light having entered the interior of the light guide
11 through the incident surface 18 is diffused by the diffusing
surface 15 and the diffused light then exits the light guide 11
through the exit surface 17.
[0045] The diffusing surface 15 is located opposite to the exit
surface 17 to extend in the sub-scanning direction. In this
embodiment, the diffusing surface 15 forms a bottom surface of the
light guide 11. The diffusing surface 15 has a plurality of light
diffusion patterns 16 provided in a row to diffuse the incident
light toward the exit surface 17. The diffusing surface 15 diffuses
the incident light, which has entered the interior of the light
guide 11 through the incident surface 18, toward the exit surface
17 via the light diffusion patterns 16. The light diffusion
patterns 16 are formed integrally with the light guide 11 from the
same material as the light guide 11.
[0046] The light source 12 is formed of, for example, an LED 121.
The light source 12 is mounted on the exterior of the incident
surface 18 of the light guide 11. In this embodiment, an example is
shown where six LEDs 121 are provided as the light source 12. The
direction of emission of light of the light source 12 toward the
interior of the light guide 11 through the incident surface 18 (the
direction of the optical axis) is a longitudinal direction of the
light guide 11, i.e., the main scanning direction.
[0047] Hereinafter, a detailed description will be given of the
light diffusion patterns 16 of the light guide 11 of the image
reading device 5 according to the one embodiment of the present
disclosure. Prior to this, light diffusion patterns of a light
guide of a general image reading device will be described
first.
[0048] The light diffusion patterns provided in a row on a
diffusing surface of such a light guide generally have a prismatic
shape rising toward the exit surface of the light guide. This is
because a mold for making the light guide can be easily machined,
resulting in reduced production costs for the light guide.
[0049] However, the light diffusion patterns having a prismatic
shape cannot diffuse direct light from the light source, i.e.,
light incident directly from the light source on the light
diffusion patterns, in the transverse direction of the light guide
(corresponding to the sub-scanning direction of the image reading
device). On the other hand, light incident on the light diffusion
patterns following one or more total reflections on the outer
periphery of the light guide after the emission from the light
source (indirect light) can be diffused in the sub-scanning
direction by the light diffusion patterns of prismatic shape, but
the quantity of indirect light in a region of the light guide near
the incident surface is small relative to the quantity of direct
light in the same region. Therefore, the light diffusion patterns
having a prismatic shape cannot diffuse a sufficient quantity of
light in the sub-scanning direction in the region of the light
guide near the incident surface. As a result, illumination
distribution in the sub-scanning direction differs between the
region of the light guide near the incident surface and a region
thereof away from the incident surface.
[0050] In this situation, if there arises a movement of the image
reading position during image reading operation or an event in
which the original document floats above the surface of the
original glass plate, the image reading position is displaced in
the sub-scanning direction. Since, with the use of light diffusion
patterns having a prismatic shape, illumination distribution in the
sub-scanning direction differs between the region of the light
guide near the incident surface and the region thereof away from
the incident surface, a displacement of the image reading position
in the sub-scanning direction may cause the read density of the
image to vary in the main scanning direction. It is conceivable to
reduce the probability of occurrence of read density variations of
an image by providing the image reading position on the original
glass plate at some distance from the incident surface of the light
guide. However, this is unfavorable in view of energy saving
because light diffused by light diffusion patterns near the
incident surface of the light guide and exiting the light guide
through the exit surface is wasted, so that the utilization
efficiency of optical energy emitted from the light source becomes
low.
[0051] Alternatively, if the light diffusion patterns in a row on
the diffusing surface of the light guide are formed to have an oval
shape rising toward the exit surface of the light guide, direct
light can be diffused in the sub-scanning direction and the
aforementioned difference in illumination distribution in the
sub-scanning direction between longitudinally different regions of
the light guide can be reduced. However, in this case, the
machining of a mold for making the light guide becomes complicated,
resulting in increased production costs for the light guide.
[0052] The inventor conducted intensive studies and reached the
above notion. Furthermore, based on the above notion, the inventor
devised light diffusion patterns 16 described below. FIG. 4 is a
perspective view showing the light diffusion patterns 16 provided
in a row on the diffusing surface 15 located inside of the light
guide 15. FIG. 5 is a perspective view showing in enlarged scale
the light diffusion patterns 16 provided on the diffusing surface
15. FIG. 6 is a view showing optical paths of light diffused by the
light diffusion patterns 16 provided on the diffusing surface
15.
[0053] The light diffusion patterns 16 are shape patterns capable
of diffusing light incident on themselves. The diffusing surface 15
has a row of a plurality of light diffusion patterns 16 formed in
alignment with one another in the main scanning direction. The row
of light diffusion patterns 16 are formed from a position on the
diffusing surface 15 a distance L (see FIG. 3) from the incident
surface 18 in the main scanning direction to an end of the
diffusing surface 15 reaching the end surface of the light guide 11
opposite to the incident surface 18.
[0054] If the light guide 11 had no light diffusion pattern, light
having entered the interior of the light guide 11 through the
incident surface 18 would propagate through the light guide 11 in
the main scanning direction while being totally reflected on the
outer peripheral surface of the light guide 11 (see L1 in FIG. 6)
and be finally guided to the end surface opposite to the incident
surface 18 without leakage. In this case, the light from the light
source 12 mounted on the incident surface 18 could not illuminate
the original document. For this reason, the light diffusion
patterns 16 are formed on the diffusing surface 15 opposite to the
exit surface 17 to reflect the incident light in the sub-scanning
direction.
[0055] As shown in FIG. 5, each light diffusion pattern 16 has a
prismatic shape rising toward the exit surface 17. In this
embodiment, a description will be given of the case where the light
diffusion patterns 16 have an approximately triangular prismatic
shape. Light entering the interior of the light guide 11 through
the incident surface 18 and then incident on the light diffusion
patterns 16 is diffused by the light diffusion patterns 16 provided
in a row on the diffusing surface 15 and the diffused light then
exits the light guide 11 through the exit surface 17 (see L2 in
FIG. 6).
[0056] In the light guide 11, the intensity of light reflected
toward the exit surface 17 by light diffusion pattern surfaces 162
of the light diffusion patterns 16 can be adjusted by varying among
the light diffusion patterns 16 the pitch in the main scanning
direction, the height, the width or so on. Therefore, by adjusting
the pitch, height, width or so on of the light diffusion patterns
16 arranged at different portions in the main scanning direction,
illuminating light exiting the different portions in the main
scanning direction can be equalized.
[0057] FIG. 7 is a view showing the relative positions of the light
guide 11 and the original glass plate 161. As described previously,
the light diffusion patterns 16 are provided in a row from a
position (P1 in FIG. 7) on the diffusing surface 15 a distance L
from the incident surface 18 (P0 in FIG. 7) in the main scanning
direction to the end (P4 in FIG. 7) of the diffusing surface 15
reaching the end surface of the light guide 11 opposite to the
incident surface 18. In other words, the light diffusion patterns
16 are provided in a row on the diffusing surface 15 in a range
represented by M1 in FIG. 7. As will hereinafter be described in
detail, the aforementioned distance L satisfies the relation
L.gtoreq.D.sup.1/2.times.8 where D represents the diameter of the
light guide 11. Since the light diffusion patterns 16 of prismatic
shape are provided not from the position P0 of the incident surface
18 but from the position P1 the distance L from the incident
surface 18, this can reduce differences in the illumination
distribution of light exiting the light guide 11, as considered in
the sub-scanning direction, among various portions of the light
guide 11 in the main scanning direction.
[0058] The image reading range in the main scanning direction on
the original glass plate 161 is set between two positions (P2 and
P3 in FIG. 7) a predetermined distance inwardly from both the ends
(P1 and P4 in FIG. 7) of the row of light diffusion patterns 16. In
other words, the image reading range on the original glass plate
161 is a range represented by M2 in FIG. 7.
[0059] Next, the effects of the above image reading device 5 will
be specifically described. FIG. 8 is a perspective view showing an
illumination device included in an image reading device of
Comparative Example 1. As shown in FIG. 8, the image reading device
110 of Comparative Example 1 is different from the above image
reading device 5 in that a row of light diffusion patterns 116 of
prismatic shape is provided immediately next to the incident
surface 18 on a diffusing surface 115 of a light guide 111.
[0060] The light source 12 including LEDs 121 emits light toward
the entire circumference of the light guide 111. Therefore, there
are produced light incident on the light diffusion patterns 116
directly from the light source 12 (direct light) and light incident
on the light diffusion patterns 116 following one or more total
reflections on the outer peripheral surface of the light guide 111
(indirect light). The direct light and indirect light differ from
each other in incident angles of light beams on the light diffusion
patterns 116 and therefore also differ from each other in the
angular distribution of exiting light beams as considered in the
sub-scanning direction. The direct light is light directly incident
on each light diffusion pattern 116 from the LEDs and, therefore,
has shallow angles with respect to the light diffusion pattern 116,
resulting in a narrow angular distribution, as considered in the
sub-scanning direction, of exiting light beams through the exit
surface. Unlike this, the indirect light is light incident on each
light diffusion pattern 116 in all directions from the entire
circumference of the light guide 111 by total reflection. In
addition, the above prismatic shaped light diffusion patterns 116,
as far as the light diffusion in the sub-scanning direction goes,
allow incident light to be reflected thereon at the same angle as
the incident angle of light beam and exit the light guide 111 at
that angle, without any deflection component in the sub-scanning
direction. Therefore, the direct light and indirect light are
different from each other in the angular distribution of light
beams in the sub-scanning direction after exiting the light guide
111, depending upon the incident angle with respect to the light
diffusion pattern 116.
[0061] The quantity ratio between the direct light and indirect
light differs among various portions of the interior of the light
guide 111 in the main scanning direction. Particularly near the
incident surface 18 in the interior of the light guide 111, the
quantity of indirect light is significantly smaller than the
quantity of direct light. In the image reading device 110 of
Comparative Example 1, since the row of light diffusion patterns
116 of prismatic shape is provided immediately next to the incident
surface 18 on the diffusing surface 115, illumination distribution
in the sub-scanning direction significantly differs between the
region of the interior of the light guide 111 near the incident
surface 18 and the region of the interior of the light guide 111
away from the incident surface 18. In other words, light exiting
the light guide 111 has different illumination distributions in the
sub-scanning direction among various portions of the light guide
111 in the main scanning direction.
[0062] Therefore, if there arises a movement of the image reading
position during image reading operation or an event in which the
original document floats above the surface of the original glass
plate 161, the image reading position is displaced in the
sub-scanning direction. Thus, deviation from reference data
determined by shading in the main scanning direction may not be
kept constant throughout the entire region in the main scanning
direction, so that an image obtained by reading the original
document may have read density variations in the main scanning
direction.
[0063] FIG. 9 is a graph showing reflected light diffusion
distributions in the sub-scanning direction produced by the light
guide 111 of Comparative Example 1. Specifically, the graph of FIG.
9 shows the illumination distributions in the sub-scanning
direction at three different positions in the main scanning
direction: a position 5 mm distant from the incident surface 18, a
position 15 mm distant from the incident surface 18, and a position
25 mm distant from the incident surface 18. The illumination values
shown in the graph of FIG. 9 are expressed as relative percentage
intensity of light at each position in the sub-scanning direction,
with 100% at a position of 0 mm in the sub-scanning direction. As
shown in FIG. 9, the illumination distribution in the sub-scanning
direction differs among the position 5 mm distant from the incident
surface 18, the position 15 mm distant from the incident surface
18, and the position 25 mm distant from the incident surface 18.
Particularly near the incident surface 18 in the interior of the
light guide 111 (at the position 5 mm distant from the incident
surface 18), the intensities of exiting light in the sub-scanning
direction are small as compared with those at the other
positions.
[0064] The inventor conducted intensive studies in this relation
and found that the quantity ratio between the direct light and
indirect light in each portion of the interior of the light guide
in the main scanning direction depends upon the diameter of the
light guide. FIG. 10 is a graph showing intensity densities of
direct light and indirect light when the diameter of the light
guide 111 is 4 mm and 6 mm. As shown in FIG. 10, with a light guide
111 of 4 mm diameter, the intensity density of indirect light
begins to be observed at 0.5 mm distance from the incident surface
18 and increases with distance from the incident surface 18. Then,
the intensity density of indirect light appears little change at
19.5 mm and greater distances from the incident surface 18. On the
other hand, with a light guide 111 of 6 mm diameter, the intensity
density of indirect light begins to be observed at 8.0 mm distance
from the incident surface 18 and increases with distance from the
incident surface 18. Then, the intensity density of indirect light
appears little change at 16.0 mm and greater distances from the
incident surface 18. To sum it up, the rate of indirect light is
substantially constant at D.sup.1/2.times.8 and greater distances
from the incident surface 18 where D represents the diameter of the
light guide 111. This relation does not depend upon the area of the
light-emitting surface of the light source 12.
[0065] In view of the above, in the image reading device 5
according to this embodiment, the row of prismatic shaped light
diffusion patterns 16 is provided on the diffusing surface 15 not
from immediately next to the incident surface 18 but from a
D.sup.1/2.times.8 or greater distance from the incident surface 18.
Since the row of prismatic shaped light diffusion patterns 16 is
provided from a position where the rate of indirect light is
substantially constant, the illumination distribution of light
exiting the light guide 11 as considered in the sub-scanning
direction can be uniform among various portions of the light guide
11 in the main scanning direction. Thus, the amount of change of
reflected light in the event of movement of the reading position
during image reading operation or the occurrence of floating of the
original document above the surface of the original glass plate 161
can be kept constant throughout the entire light guide 11 in the
main scanning direction, which makes it less likely to cause the
read image to have read density variations.
[0066] It is conceivable, in the configuration of Comparative
Example 1, to reduce the probability of occurrence of read density
variations of an image by providing the image reading range on the
original glass plate at some distance from the incident surface 18
of the light guide 111. However, this is unfavorable in view of
energy saving because light diffused by light diffusion patterns
116 near the incident surface 18 of the light guide 111 and exiting
the light guide 111 through the exit surface 17 is wasted as not
being used for image reading, so that the utilization efficiency of
optical energy emitted from the light source 12 becomes low.
[0067] Unlike the above, in the image reading device 5 according to
this embodiment, the row of prismatic shaped light diffusion
patterns 16 is provided from a position where the rate of indirect
light is substantially constant. Therefore, the image reading range
on the original glass plate 161 can be provided in a range
corresponding to the range within which the light diffusion
patterns 16 are provided. Hence, light diffused by the light
diffusion patterns 16 and exiting the light guide 11 through the
exit surface 17 can be efficiently used for image reading and,
thus, the utilization efficiency of optical energy emitted from the
light source 12 is high.
[0068] As in a light guide 211 of Comparative Example 2 shown in
FIG. 11, if light diffusion patterns 216 provided on a diffusing
surface 215 of the light guide 211 have an oval shape rising toward
the exit surface of the light guide 211, direct light may be able
to be diffused in the sub-scanning direction and differences in
illumination distribution in the sub-scanning direction among
different portions of the light guide 211 may be able to be
reduced. However, in this case, the machining of a mold for making
the light guide 211 becomes complicated, resulting in increased
production costs for the light guide 211.
[0069] Unlike the above, in the light guide 11 according to this
embodiment, the light diffusion patterns 16 provided on the
diffusing surface 15 have a prismatic shape rising toward the exit
surface 17. In the case of the light diffusion patterns 16 of
prismatic shape, a mold for making the light guide 11 be easily
machined, resulting in reduced production costs for the light guide
11.
[0070] The present disclosure is not limited to the above
embodiment and can be modified in various ways.
Modification 1
[0071] Although in the above embodiment a structure has been
described in which only one end surface of the light guide in the
main scanning direction provides an incident surface and the light
source emits light from one longitudinal end of the light guide,
the present disclosure is not necessarily limited to this
structure. For example, another structure may be employed in which
both end surfaces of the light guide in the main scanning direction
provide incident surfaces and light sources mounted on both the end
surfaces emit light to the interior of the light guide.
[0072] FIG. 12 is a view showing the relative positions of a light
guide 311 and an original glass plate 161 in an image reading
device of Modification 1. As shown in FIG. 12, light sources 12A,
12B are mounted on both the end surfaces of the light guide 311. A
row of light diffusion patterns 316 is provided from a position (P1
in FIG. 12) on a diffusing surface 315 a distance L from one
incident surface 18A (P0 in FIG. 12) in the main scanning direction
to a position (P6 in FIG. 12) thereon a distance L from the other
incident surface 18B (P4 in FIG. 12) in the main scanning
direction. In other words, the light diffusion patterns 316 are
provided in a row on the diffusing surface 315 in a range
represented by M3 in FIG. 12. The image reading range on the
original glass plate 161 is set between two positions (P2 and P5 in
FIG. 12) a predetermined distance inwardly from both the ends (P1
and P6 in FIG. 12) of the row of the light diffusion patterns 316.
In other words, the image reading range on the original glass plate
161 is a range represented by M4 in FIG. 12.
Modification 2
[0073] The light guide described in the above embodiment can have a
U-shape. FIG. 13 is a side view showing a light guide 411 included
in an image reading device of Modification 2. As shown in FIG. 13,
the light guide 411 is provided at one end with an incident surface
418 through which light emitted from a light source 412 enters the
light guide 411, and the one end thereof provided with the incident
surface 418 is curved in a direction away from the exit surface 417
of the light guide 411. A curved reflective surface 419 is provided
between the incident surface 418 and the exit surface 417. Light
having entered the interior of the light guide 411 through the
incident surface 418 is totally reflected at the reflective surface
419 and progresses into a middle region of the light guide 411. The
light having progressed into the middle region of the light guide
411 is diffused by light diffusion patterns 416 provided on a
diffusing surface 415 and exits the light guide 411 through the
exit surface 417.
[0074] In this case, the row of light diffusion patterns 416 on the
diffusing surface 415 is formed, like the above embodiment, from a
distance L from the incident surface 418. Since the end of the
light guide 411 provided with the incident surface 418 is curved in
a direction away from the exit surface 417, the distance L0 from
the incident surface 418 to the beginning of the row of light
diffusion patterns 416 is smaller than that in the light guide 11
in the above embodiment. Therefore, the dimension of the light
guide 411 in the main scanning direction can be reduced, resulting
in size reduction of the image reading device.
Modification 3
[0075] Although the above embodiment includes LEDs 121 as the light
source 12, the light source used in the present disclosure is not
limited to LEDs and can include various types of light sources so
long as they can emit light in the main scanning direction from the
end surface of the light guide 11 toward the interior thereof.
[0076] Various modifications and alterations of this disclosure
will be apparent to those skilled in the art without departing from
the scope and spirit of this disclosure, and it should be
understood that this disclosure is not limited to the illustrative
embodiments set forth herein.
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